1. Field of the Invention
The present invention relates to a light emitting device such as a light emitting diode and a laser diode that has an excellent heat release capability, a method of manufacturing the light emitting device, and a lighting equipment using the same, in which the light emitting device is for example in the form of a light emitting diode provided with a high-electric power and high-optical power light emitting element.
2. Related Art
As an typical example of the light emitting device, it can be cited an electronic device such as a light emitting diode and a laser diode. Of them, the light emitting diode (hereinafter referred to an LED) is provided with a light emitting element that is powered so as to emit light. At the time of light emission, the light emitting element also generates heat, causing temperature rise of the LED.
An LED is recently used as a display device for an indicator of an electric appliance, a liquid crystal backlight of a mobile phone thanks to the development of a blue LED, a white LED and the like. Also, an LED is expected to be widely used for a lighting equipment such as an interior illumination, automobile lighting or traffic signal because of its high light emission efficiency and improved brightness. Thus, a demand for a high optical power LED is increased so as to make an LED applicable to such a lighting equipment. The application of the LED in a new field is accompanied with a problem to cause temperature rise of an LED due to increased power supply.
For the light emitting device such as a high electric power and high optical power LED as mentioned above, a ceramic material is sometimes used for a package part that is tolerable against such temperature rise.
A light emitting device with such a packaging ceramic part is provided with for example a metallic part made of metal for heat radiation that is mounted to the ceramic part, allowing heat from a semiconductor element such as a light emitting element to be instantly transferred to the metallic part by heat conduction and to be dispersed through the metallic part for heat release with high efficiency from the surface of the metallic part to a heat release section or part, thus preventing the semiconductor element from being heated over a given performance guarantee temperature.
For producing the light emitting device with the heat-release metallic part and the packaging ceramic part, both parts are generally bonded together via an adhesive. The bonding of these parts is conventionally made by a brazing technique using a brazing material such as silver (Ag), gold (Au), copper (Cu), zinc (Zn) or cadmium (Cd), which is generally used as the adhesive for this purpose.
The light emitting device with the heat-release metallic part bonded to the packaging ceramic part by brazing may cause stress in these parts as the temperature rises, due to difference in coefficient of linear expansion therebetween, resulting in the likelihood of causing warping of these parts or break (crack) of the ceramic part. Hitherto, in order to avoid this problem, it is selected materials used for these ceramic part and metallic part to have approximate coefficients of linear expansion for bonding.
As the ceramic material, generally used are such as aluminum nitride (AlN) and aluminum oxide (Al2O3). As the metallic material, generally used are such as copper-tungsten composite (CuW), and copper-molybdenum composite (CuMo, CuMoCu). The followings are the coefficient of linear expansion of each material.
Ceramic MaterialAlN4.5 × 10−6Al2O36.7 × 10−6Metallic MaterialCuW6.5 × 10−6 (W-10:89W, 11Cu)CuMo7.0 × 10−6 (CM-15:85Mo, 15Cu)CuMoCu8.9 × 10−6 (CMC111)
wherein CuMoCu (CMC111) is made up of two Cu plates and an Mo plate held therebetween and bonded together with the layer ratio of Cu:Mo:Cu=1:1:1.
The metallic materials as described above, such as CuW, CuMo and CuMoCu respectively have thermal conductivities (specifically, CuW: 180 W/mk, CuMo: 160 W/mk, and CuMoCu: 232 W/mk), which are lower than other metallic materials having a relatively high thermal conductivity (typically, Cu: 393 W/mk). Therefore, while there is a demand for using a metallic material such as Cu having a relatively high thermal conductivity for a heat-release metallic part in a recent high-electric power and high-optical power light emitting device such as an LED used in a lighting equipment, a metallic material such as Cu, a coefficient of linear expansion of which is 17.0×10−6, is greatly different in coefficient of linear expansion from the ceramic material, which results in the likelihood of causing warping or break (crack) of the ceramic part due to stress caused as the temperature rises.
On the other hand, a high-electric power and high-optical power LED is required to meet the following demand. That is, in an LED, light emitted from the side (not main sides) of a light emitting element is hard to be utilized and therefore light is hard to be emitted with high efficiency. For example, where a ceramic part is used as a packaging part, light emitted from the side of the light emitting element is reflected on the ceramic part and then radiated to the outside, and this reflection leads to deteriorated efficiency in utilization of light. Where an LED is utilized in a lighting equipment or the like with a corrective lens or the like for correction of light, light emitted from the side of the light emitting element and then reflected on the ceramic part invites occurrence of inconsistent light correction. Conventionally, plural LEDs are provided to constitute plural light sources, thereby limiting the influence of this inconsistent light correction as much as possible. However, a recent high-electric power and high-optical power LED can be utilized as a single light source. Accordingly, a recent high-electric power and high-optical power LED is required to achieve effective and efficient utilization of light emitted from the side of the light emitting element while limiting inconsistent light correction.
In the conventional lighting equipment utilizing a light emitting device such as an LED, electrical connection and fixation with the light emitting device is made by soldering, or calking of a lead frame or the like. Accordingly, the lighting equipment utilizing the light emitting device, in which heat release to an external wiring substrate is made via a soldered portion or lead frame, achieves only a limited transfer of heat and hence insufficient heat release capability. Therefore, it is not possible to make a large electric current flow through the lighting equipment, thus making it impossible to achieve a high brightness lighting equipment.
Also, once a light emitting device is incorporated into the lighting equipment by soldering or calking with an external wiring substrate, it is difficult to remove only the light emitting device from the lighting equipment and repair the same.
Another disadvantage associated with the conventional lighting equipment, in which a conductive pattern provided on a main side of the light emitting device is partially soldered or calked with an external wiring substrate, is that the light emitting device is likely to be easily subjected to an adverse influence due to mechanical vibrations coming from the outside. That is, the calking of the conductive pattern of the light emitting device may easily cause variation in optical characteristics due to unintentional rolling or movement of the light emitting device in the lighting equipment, and the soldering of the light emitting device may easily cause defect in electrical connection with an external electrical circuit substrate.
It is a first object of the present invention to provide a light emitting device with a heat-release metallic part made of metal and a packaging ceramic part made of ceramics, which are bonded together with an adhesive, and a method of manufacturing the same, which are capable of preventing a problem due to the difference in coefficient of linear expansion between the metallic part and the ceramic part, such as a problem of causing stress as the temperature of the metallic part and the ceramic part rises, which leads to warping or break (crack) of the ceramic part, and therefore allowing a metallic material having a good thermal conductivity to be used, thus achieving a high-electric power and high-optical power device characteristic never achieved before.
It is a second object of the present invention to provide a light emitting device with a heat-release metallic part made of metal and a packaging ceramic part made of ceramics, which are bonded together with an adhesive, which is capable of achieving effective and efficient utilization of light emitted from the side of the light emitting element while limiting inconsistent light correction, where the light emitting device is provided in the form of an LED with a light emitting element.
It is a third object of the present invention to provide a highly reliable lighting equipment thanks to improved heat release capability, allowing it to be used in place of a conventional lighting equipment such as a lamp and fluorescent lamp.